Safety and health in mines research advisory board

Annual Review 2000

CONTENTS

INTRODUCTION

The Safety and health in mines research advisory board (SHMRAB) is one of
the Health and Safety Commission's (HSC) independent advisory bodies. During
2000 it was reconstituted as a sub-committee of the Deep Mined Coal Industry
Advisory Committee (DMCIAC). SHMRAB is chaired by Her Majesty's Chief Inspector
of Mines and has up to ten members representing employers and employees in
the British coal mining industry and eight adviser members with relevant expertise
in research or mining. Current members are listed in the appendix along with
others who contributed to SHMRAB's work during 2000.

As well as advising HSC and DMCIAC, SHMRAB's remit includes providing information
to the deep mined coal industry on research matters relevant to improving
health and safety standards in the industry. This review summarises progress
made during 2000 on research within SHMRAB's remit.

FIRE AND EXPLOSION

Ventilation-Controlled Fires

The Health and Safety Laboratory (HSL) began work on this project in September
2000. It is jointly funded by the European Coal and Steel Community (ECSC)
and the Health and Safety Executive (HSE) mines and railways inspectorates.
The objectives of the work are to establish whether ventilation-controlled
fires, those fires supplied with less than the stoichiometric air requirement,
can occur in tunnels and to investigate their characteristics, particularly
their response to changes in ventilation. Fires will be examined in terms
of downstream temperature, the rate of fire growth, smoke production and CO/CO2
ratio. The latter two parameters may be significantly enhanced in ventilation-controlled
fires and significantly increase the tunnel fire hazard. There may also be
implications for the way such fires are fought in tunnels. The work will also
provide a data base to assist the modelling of such fires.

Effort during 2000 has been devoted to a literature search on experimental
tunnel fires which have grown to ventilation control. This has identified
a very limited range of publications indicating that little work has been
attempted in the area. Work has also begun on designing the experimental programme
to be carried out at the Buxton fire gallery in 2001. Instrumentation has
been decided and is being assembled .

Pressure Balancing for the Combat of Tunnel Fires

Following the suggestion of a member of the public that pressure balancing
would have been an effective means of combating the fire in the Channel Tunnel
in November 1996, a paper study was undertaken to examine the possibility.
Partially as a result of this an experimental investigation has begun.

A rig has been assembled at approximately 1:33 scale, comprising a straight
aluminium tube furnished with 'T'-pieces, ventilation fans and butterfly valves
at each end. Pressure and temperature measurements can be taken at four positions
in the duct. Located at the centre of the duct a steel fire zone is equipped
with a fuel tray mounted on load cells. The intention is to set a fire and
then, by adjusting the fans and valves in combination, achieve a balanced
ventilation condition and examine for reduction in fire intensity from the
fuel burn rate as measured by the load cells. Preliminary results indicate
that the required pressure balancing effect is not achievable but further
work is proceeding.

CFD Modelling of Gas Flows in Coal Mine Goafs.

This HSL project began in April 1999 and the results of the initial work
were reported last year. It is co-funded by HSE and the ECSC programme. The
main objectives are to use computational fluid dynamics (CFD) modelling to
improve understanding and control of methane emissions from the goaf and longwall
faces, as well as to use CFD to improve understanding and control of spontaneous
heating in the goaf by optimising inert gas injection systems. An important
aspect of the work is to combine the outputs of rock mechanics modelling with
the modelling by CFD.

During this year, the development of a 3-D CFD model of ventilation and methane
flows at a longwall panel (as detailed last year) has continued. In addition
the rock mechanics work, subcontracted to Nottingham University, has been
completed. Models have now been developed to predict stress and deformation
of a longwall panel and values for rock permeability after mining has occurred.
In addition a CFD methodology has been developed to predict permeability in
the regions of fractured rock. Work is continuing to incorporate the rock
mechanics predictions into the CFD models. The project is due for completion
in March 2002.

Effective Design and Management of Firedamp Drainage

Wardell Armstrong was commissioned by HSE to review the state-of-the-art
on firedamp drainage and its application in UK coal mines. The work which
comprised a worldwide literature review, visits to selected UK mines and discussions
with HSE mines inspectors.

The report includes a free-standing annex in the form of a guidance document
which sets out what the researcher considers is good practice, structured
in accordance with current HSE thinking on safety management processes. It
has been published as Contract
Research Report 326/2001 on HSE's website and in hard copy from HSE Books.

Ignition Control on Longwall Faces

IMC Technical Services Ltd (IMC-TS) completed work on this ECSC-sponsored
project, progress on which was reported in last year's review. The main conclusions
were:

the presence of high volatile coal dust, up to a concentration of 2g/m³,
was found to have no measurable influence on the lower ignition threshold
concentration of methane, when ignited by a frictional ignition source generated
by a blunted pick cutting sandstone. Variations in the lean explosive limit
concentration were identified with changes in humidity (lower concentrations
being ignitable at lower humidity levels), and with ignition source energy.
At a constant 85% humidity, minimum ignitable concentrations of 5.5%, using
a spark plug with an ignition energy of approximately 100mJ and 4.7%, with
a source generated from a blunt pick striking sandstone, were observed.

Fire Effects and Impacts

IMC-TS started work on a new ECSC sponsored project on fire effects which
is allied with an HSE sponsored project being conducted by Cerberus Ltd. and
which concerns the feasibility of bench-scale model testing for conveyor belt
approvals. The objectives of the ECSC project are to examine the close proximity
effects and impacts of fires, with respect to ventilation flows and heat distribution,
to aid the early detection and prediction of fires.

To fulfil the objectives of both programmes of work, an intensive series
of tests was conducted in IMC's fire test gallery at Swadlincote, prior to
closure of this facility in September 2000. Initially, a series of calibration
tests were carried out at nominal gallery air speeds of 0.5, 1.0, 1.5 and
2.0m/s using various arrangements of propane burners while monitoring the
effects on upstream air velocities and downstream air temperatures using arrays
of instruments in the gallery cross-section. Downstream oxygen levels were
also monitored. The calibration tests were followed by assessments of three
types of conveyor belting using the standard UK belt approval test method
- an approved Type 10 belt, a nitrile belt which would be expected to be a
marginal approval failure and a non-fire resistant rubber belt. An array of
thermocouples attached to the belt were used to monitor the progress of the
belt fire in each test. Initial analysis of the results has shown a wide range
of effects, the most notable of which was a progressive change in airflow
patterns as airspeeds through the gallery were increased. At lower airspeeds,
the presence of a fire caused an increase in air velocities near floor level,
upstream of the fire, while those near roof level decreased, or even reversed
when heat input was high. At higher general airspeeds, these effects became
much less significant with little change in measured velocities upstream of
the fire at a velocity of 2m/s. Downstream of the fire, highest temperatures
were always recorded close to roof level although the temperature distribution
with height became more even as airflows through the gallery increased. There
was also some experimental variation in the way that the various belts burned,
even between repeat tests, most frequent of which was the front edge of the
belt sample curling up, influencing the application of heat by the propane
burner.

Remaining work on the ECSC project, involving the development of a CFD model
to predict the effects of fires in underground roadways is being handed back
to the project co-ordinator, who currently envisages completion of the project
work by Nottingham University and DMT. Cerberus is continuing work on the
second phase of the HSE project at Fenner Ltd's facilities at Hull.

Testing of Breathing Apparatus

The programme of tests at HSL on the modified method of setting the relief
valve opening pressure on the Selected Elevation Flow Apparatus (SEFA) breathing
apparatus has been completed. Provided the actuating arm of the mechanism
is undamaged, the new setting method does not affect the safety or performance
of the breathing apparatus. The potential problem first came to light on a
set where the actuating arm was damaged. Inclusion of examination of the actuating
arm condition in routine testing and maintenance has been recommended.

The programme of random check-testing of SEFA sets by HSL continues, as a
means of monitoring their condition and maintenance.

Difficulties are emerging over the continuing supply of spares and components
to maintain this apparatus in service. The manufacturer has indicated his
intention to stop supporting the equipment; it has not been manufactured for
some years and remaining stocks of spare parts are limited. In view of this,
it is recommended that alternative forms of breathing apparatus are investigated
for Mines Rescue use.